Third Law
Easychemistry
Third Law of Thermodynamics states entropy of a perfect crystal at 0 K is:
Select the correct option:
Solution
Incorrect! Answer:
Zero
- Entropy and Temperature: Entropy measures molecular disorder. At lower temperatures, thermal motion decreases, and disorder drops.
- Third Law Postulate: The entropy of a pure, perfectly crystalline substance is exactly zero at the absolute zero of temperature (0 Kelvin).
- Why?: In a perfect crystal, there is only one possible microstate: every atom is in its exact specified lattice position. According to Boltzmann's formula S=klnW, when W=1, S=0.
- Reference State: This law allows scientists to define a 'Standard Entropy' (an absolute scale) for all substances.
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About This Question
- Subject
- chemistry
- Chapter
- chemical thermodynamics
- Topic
- third law
- Difficulty
- Easy
- Year
- 2025
Solution
Correct Answer:
Zero
- Entropy and Temperature: Entropy measures molecular disorder. At lower temperatures, thermal motion decreases, and disorder drops.
- Third Law Postulate: The entropy of a pure, perfectly crystalline substance is exactly zero at the absolute zero of temperature (0 Kelvin).
- Why?: In a perfect crystal, there is only one possible microstate: every atom is in its exact specified lattice position. According to Boltzmann's formula S=klnW, when W=1, S=0.
- Reference State: This law allows scientists to define a 'Standard Entropy' (an absolute scale) for all substances.
This easy difficulty chemistry question is from the chapter chemical thermodynamics, covering the topic of third law. It appeared in the 2025 exam.
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